Stressed plants start to flower earlier

Jul 03, 2019

A botanical research team from Kiel describes the effect of certain proteins on the time of plant flowering

One of the central tasks in botanical research is the study of the plant mechanisms involved in regulating the time of flowering. All plants flower when they are transitioning from the growth stage to reproduction. The time when this transition takes place is relevant, for instance, with respect to the adaptability of plants to changing environmental conditions, especially in the context of climate change. The time of flowering is also of great importance for crop cultivation, as it determines harvest times and crop yields. The underlying processes are therefore also of great interest for breeding crops. Scientists all over the world are working intensively on investigating all of the components involved in controlling the time of flowering. A research team from the Botanical Institute at Kiel University has now characterised a previously unknown component of this regulation: taking the model plant Arabidopsis thaliana as an example, the researchers from the Department of Genetics and Molecular Biology identified a relationship between a specific protein and the time of flowering. This so-called Poco1 protein occurs in a plant cell organelle, the mitochondria, whose role in the regulation of flowering time had not been analysed in detail before. The researchers from Kiel University found out that by switching off the gene responsible for the protein, the plant starts to flower much earlier. The regulation influenced by Poco1 may also be related to unfavourable environmental conditions. The scientists, who are also actively involved in the newly founded Kiel Plant Center (KPC), published their results in the current issue of The Plant Journal, a renowned scientific publication.

An equation with many variables
The point in time when a plant changes from the so-called vegetative to the reproductive phase and begins to flower is mainly regulated by various interconnected genetic pathways. External influences such as hours of daylight or temperature also affect the time of flowering. In order to investigate the role of the Poco1 protein in this interaction, the researchers from Kiel University inactivated the Arabidopsis gene responsible for it. The plants that were modified in this way started to flower an average of five days earlier than the wild types, irrespective of the environmental conditions.

In order to confirm that this effect on the regulation of flowering time is really due to the protein, the research team carried out a number of further tests. “We took the modified plants from our experimental design and carried out a so-called genetic complementation test,” explains Hossein Emami, PhD student in the Department of Genetics and Molecular Biology. “As a result, the plants started to flower again at normal flowering time. This was another indication that the original change was due to the Poco1 protein,” Emami adds.

The comparison of root growth also points in the same direction: while in the Arabidopsis wild types a certain control mechanism stops the length growth of the roots at the transition to the reproductive phase, this signalling pathway is disturbed in the Poco1 plants. As they lack sufficient quantities of the substances contributing to this regulation, they have significantly longer roots than wild plants. “This difference compared to wild plants also seems to have been caused by the Poco1 protein,” Emami emphasises. “By downregulating the signals, this protein promotes root growth and weakens the plant’s inhibition to flower,” he adds.
Unfavourable environmental conditions affect the time of flowering.

In order to further analyse these relationships, the KPC research team investigated the interaction of mitochondria and the plant nucleus with regard to the regulation of the flowering time. They first investigated the most important physiological functions of the mitochondria and found that they were significantly disturbed in the Poco1 plants. They were found to have lower cellular respiration, a lower energy content and a higher occurrence of cell-damaging so-called free radicals in comparison with the Arabidopsis wild types. These physiological deviations are probably associated with a signal from the mitochondria to the plant nucleus, which influences the mechanism underlying earlier flowering under stress conditions.

“Unfavourable environmental conditions such as drought can cause plants to flower earlier than normal in order to ensure their reproductive success,” stresses Professor Frank Kempken, KPC member and head of the Department of Genetics and Molecular Biology. “We therefore assume that mitochondrial proteins such as Poco1 provide crucial signals and thus play a more important role in plant adaptation to environmental stress than we had previously thought,” Kempken adds. In plant breeding, these findings could be used as a basis to regulate the flowering time of important crops in such a way that they can continue to thrive even under drastically changed climatic conditions.